The postoperative management of patients having undergone total hip arthroplasty or endoprosthetic hemiarthroplasty usually includes measures to prevent early dislocation. Adduction especially increases the risk of dislocation and hence pillows or splints which maintain the hip in an abducted position are commonly employed. Such devices are commercially available from a variety of manufacturers. Despite variations in base material, usually some form of foam rubber, and covering, e.g. cloth, vinyl, most pillows have basically the same design. This includes a triangular or rhomboid shape such that the apex fits between the thighs proximally and the broader base fits between the ankles, thereby maintaining the desired abduction. Retention straps attached to the pillow secure it in place by encircling the legs above and below each knee.
This design has proven quite effective in maintaining the desired position of abduction. However, several problems have been associated with its use, ranging in magnitude from minor inconveniences to major complications with potentially permanent impairment of function. These include pressure sores of the heels, stretch injuries to soft tissues, and difficulties with elimination and perineal care.
With respect to the first of these it will be noted that current designs of abduction pillows utilize retention straps above and below the knees. Because the pillow itself is generally fairly rigid, it acts as a splint to maintain the knee in full extension. With the leg cinched against the pillow, a situation can arise in which the buttock proximally and the heel distally are the only firm points of contact between the leg and the bed. The heel then supports a large portion of the weight of the leg, distributing it over the very small surface area of the heel.
This is aggravated by the fact that in the immediate post operative state, the patient is usually heavily sedated, and often is given high doses of narcotic analgesics. Normal protective sensation can be markedly impaired by these medications. The situation is even more dramatic for the patient in whom spinal or epidural anesthesia has been used, in that they may have no protective sensation to the lower extremities for hours.
Combined with the immobility imposed by the abduction pillow and sedating medications, the stage is set for pressure injury to the backs of the patient's heels. Only a few hours of excessive pressure to skin with compromised protective sensation is sufficient to initiate tissue damage. Degrees of injury are similar to those applied in describing burns. In the mildest form, this amounts to reddening and an uncomfortable burning sensation for the patient. Next in severity is blistering of the skin. This usually eventuates in a sizable vesicle which then breaks and is quite painful. In the most severe form of injury there can be full thickness skin loss and eschar formation necessitating debridement and later skin grafting.
As indicated, stretch injuries to soft tissues comprises another potential problem associated with conventional abduction pillow use. Thus, as a result of the disease process underlying the necessity for total hip replacement, there is often shortening of the involved extemity as a result of loss of the joint space, collapse of the femoral head, protrusion of the femoral head centrally through the acetabulum or subluxation of the hip. Whatever the mechanism, the shortening can amount to several centimeters in severe cases. Along with these changes in the bones, there are parallel changes in the soft tissue envelope surrounding the hip joint such that secondary shortening of the muscles, nerves, blood vessels and fascial sleeves takes place.
At the time of surgery, a major objective is the restoration of normal leg length. Whereas this can be accomplished within the time span of the operation, the soft tissue changes described above, which probably developed over a period of years, require several weeks to stretch out and accommodate the new leg length. Several muscles, particularly those in the hamstrings group, cross both the hip and knee joints, and have maximal tension placed upon them when the knee joint is obligated to a position of full extension. Such is the case with current designs of abduction pillows.
This tension on major muscle groups and fascial sleeves can result in severe muscle spasm and pain for the patient. The major neurovascular structures of the lower extremity are subjected to the same stretching phenomena. Patients in whom neurovascular status of the lower extremity was completely intact on the evening of a surgery in which the leg was lengthened, may be found to have incurred a peroneal palsy the following morning after immobilization in an abduction pillow over night with the knee in full extension. Damage to this division of the sciatic nerve can be permanent. In similar fashion, vascular compromise of the lower extremity can result from leg lengthening followed by post operative immobilization with the knee in extension. This is particularly so in the patient with significant atherosclerotic peripheral vascular disease.
Lastly, current abduction pillow design inevitably results in difficulties with elimination and perineal care. These arise from the fact that conventional abduction pillows fit quite high between the thighs, such that in order to use a bedpan or a urinal, it is necessary to remove the retention straps and either completely remove the pillow or to slide it distally a significant distance. The same holds true for the performance of routine perineal care.